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What is Periodic Ophthalmia?

The condition cannot be cured, but the progression can be slowed by giving immediate and aggressive treatments. Your horse will need to be routinely treated by your veterinarian. If you suspect that your horse has developed periodic ophthalmia, contact your veterinarian quickly for a definitive diagnosis and the proper treatments.

Periodic ophthalmia in horses is also known as equine recurrent uveitis, ERU or moon blindness. It is considered to be one of the most common types of eye problems in horses. Periodic ophthalmia is where your horse’s immune system begins attacking the tissues within the eye. It will cause your horse to eventually go blind.

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Symptoms of Periodic Ophthalmia in Horses

You should be doing a daily assessment of your horse so you can quickly treat any problems that present. This includes a thorough check of your horse’s eyes for any changes that could mean periodic ophthalmia is developing. If you notice the slightest change to your horse’s eye, err on the side of caution and have your veterinarian take a look. Symptoms of periodic ophthalmia that you should look for include:

Swelling of the eyelid

Watery eyes

Pus coming from the eye

Redness of the eye

Constriction of the pupil in the dark

Squinting

Cloudiness of the eye

Sensitive to light

Sudden blindness

Causes of Periodic Ophthalmia in Horses

There are several causes of periodic ophthalmia in horses; this is what makes the disease so volatile. Some researchers believe that an impairment of the blood aqueous barrier within the iris and the ciliary vasculature causes inflammation to occur.

The most common cause, however, is a bacterial infection, leptospirosis, that enters through the mucus membranes of the eye. The bacteria pass to your horse through contact with the infected animal’s urine. There are other bacteria that can cause infections, leading to periodic ophthalmia. Those include brucella, Escherichia coli, rhodococcus equi and streptococcus equi.

Trauma can also lead to the development of periodic ophthalmia, as can allergies. When certain allergens, such as ragweed and pollen are high, the number of cases of periodic ophthalmia rises.

Diagnosis of Periodic Ophthalmia in Horses

Your veterinarian may refer you to a specialized equine ophthalmologist for a definitive diagnosis of periodic ophthalmia. The diagnosis typically can only be made after the horse has experienced several bouts of periodic ophthalmia in at least one eye.

Your veterinarian will need a complete medical history as well as what symptoms have presented and how often they occur. Keeping notes of what symptoms and when they occur will help your veterinarian when making a diagnosis.

Periodic ophthalmia is a progressive eye disease that will eventually lead to blindness. Immediate and aggressive treatments may slow the progression and could possibly stop it from progressing to complete blindness.

Treatment of Periodic Ophthalmia in Horses

While periodic ophthalmia is incurable, there are treatments available that can slow the progression of the disease. Your veterinarian will prescribe an aggressive treatment plan designed to slow, and in some instances completely stop, the progression.

When your horse has an active flare up, meaning there is an increase in the inflammation within the eye, the symptoms must be quickly treated to help control the pain levels and minimize the damage to the eye structure.

Most treatments will include topical creams that are anti-inflammatory and steroidal. Systemic immunosuppressive medications, anti-inflammatory medications and steroids may also be used. Each treatment cycle will typically last about four weeks.

During treatments, you may need to hospitalize your horse and have a subpalpebral lavage catheter in the eye to administer the appropriate medications. A subpalpebral lavage catheter is a tube that is run over the top of your horse’s head and inserted through the upper eyelid. The medications are administered directly onto the eye without your horse becoming head shy from the administration of the medications.

There some teaching hospitals that have begun experimenting with new surgical techniques. This surgery is being used to provide longer control of the periodic ophthalmia. There are only a few ophthalmologic surgeons who are able to perform this procedure.

There are some instances where the disease has progressed significantly and blindness has already occurred. Even though your horse may be blind, they can still experience significant pain. Surgical removal of the eye is then required to eliminate the pain that they horse is feeling.

Recovery of Periodic Ophthalmia in Horses

Since periodic ophthalmia is incurable, the only hope is to slow the progression of the disease. In some cases, the disease is able to be stopped although your horse will still remain affected by it but blindness is less likely to occur.

Prevention is important and many veterinarians are now recommending a leptospirosis vaccine along with good stable hygiene and management. Keeping stalls cleaned, removing any stagnant water and keeping grains properly stored will help reduce the risk of periodic ophthalmia.